PHOENIX — On “Weather and Science Day” at Chase Field, Dodgers manager Dave Roberts and his staff were thinking about weather and the inexact science of a starting rotation.

After an off day Thursday, the Dodgers start a three-game series in San Francisco on Friday where rain is almost a certainty – Weather.com has called its shot, putting the chance of rain at 100 percent. The only certainties in the Dodgers’ pitching plans are that left-hander Clayton Kershaw will start Sunday on normal rest – and someone will get skipped.

“If there is a rainout then we have to kind of pivot and figure out who we want to throw,” Roberts said in sunny Arizona on Wednesday. “There’s some moving parts where we don’t have a whole lot of clarity.”

Both right-hander Kenta Maeda and left-hander Hyun-Jin Ryu are candidates to be skipped in the rotation this weekend. Maeda was available in the Dodgers’ bullpen Wednesday “for coverage,” Roberts said, after Dodgers relievers pitched 23-2/3 innings in the first six games of the season, almost half of them (10-2/3) in Monday’s 15-inning game.

The right-hander was not needed in the 3-0 loss and will make the start Friday in San Francisco – “weather pending,” Roberts said after Wednesday’s game.

Left-hander Rich Hill is penciled in to start Saturday’s game with Ryu getting skipped in the rotation. A rainout Friday could result in a doubleheader – though the teams are more likely to make the game up later in the season – and muddle the Dodgers’ rotation. Both Maeda and Ryu could emerge from the weekend without another starting assignment until well into next week. The Dodgers play just five games in the next eight days with off days coming on Monday and Thursday of next week.

“I appreciate the way that there are off days,” Roberts said. “But where they are for us right now it’s not ideal. I guess it beats (playing) 21 days in a row.”

FIRST BASE

Roberts said he wanted to give each of his regulars a day off as the Dodgers started the season with seven consecutive games. He held to his promise – except with Yasiel Puig. Puig has started each of the Dodgers’ first seven games.

Cody Bellinger got his first day off Wednesday. Kike’ Hernandez started in his place. It was Hernandez’s third big-league start at first base. He started there twice last season (once in June, once in July) and has played there some during winter ball.

“He can defend over there,” Roberts said. “He’s played, maybe not a lot of games there in the majors, but in his history in the minors and winter ball. So he feels comfortable over there.”

Roberts said Hernandez could make intermittent starts at first base this season. The Dodgers have limited options for backup first basemen – the left-handed Chase Utley and right-handed hitters Kyle Farmer and Hernandez. Roberts said this spring Hernandez had earned more playing time. Spelling Bellinger at first base occasionally against left-handed pitchers could give Hernandez some more at-bats.

“I think so. I think if you look at when we would give Cody a day, it would be potentially against a left-hander,” Roberts said. “With what Kike’s done at the end of last year, throughout the spring, I really just see there’s been a change in approach, mechanics. When he plays he always seems to do something to help you win a baseball game. To have the versatility and the openness from him really makes me feel confident. He’s a guy I just really try to find ways to get him in the lineup.”

ALSO

Roberts said left-hander Julio Urias took a few days off from his throwing program after having his tonsils removed. Urias had progressed to throwing on flat ground. He has not been cleared to throw off a mound yet and is not expected to return until the second half of this season after undergoing major shoulder surgery last June. … Justin Turner (wrist) and Tom Koehler (shoulder) will stay in Arizona when the Dodgers leave for San Francisco and continue their rehabs at the training complex in Glendale. … Top pitching prospect Walker Buehler is scheduled to start the season opener for Triple-A Oklahoma City on Thursday.

Bill Plunkett has covered everything from rodeo to Super Bowls to boxing (yeah, I was there the night Mike Tyson bit Evander Holyfield's ear off) during a career that started far too long ago to mention and eventually brought him to the OC some time last century (1999 actually). He has been covering Major League Baseball for the Orange County Register since 2003, spending time on both the Angels and Dodgers beats.